"My daughter Ivanka has been treated so unfairly by @Nordstrom. She is a great person -- always pushing me to do the right thing! Terrible!" he tweeted.

Nordstrom said last week that it would no longer carry Ivanka Trump's line of clothing and accessories because of "brand performance."

The tweet, which was later retweeted by the official @POTUS account, raised eyebrows among ethics experts.

Larry Noble, the general counsel of the Campaign Legal Center, a nonpartisan organization of election law experts, said Trump's tweet was "totally out of line."

"He should not be promoting his daughter's line, he should not be attacking a company that has business dealings with his daughter, and it just shows the massive amount of problems we have with his business holdings and his family's business holdings," Noble said Wednesday.

Press Secretary Sean Spicer defended the president's use of the @POTUS handle to discuss his daughter's business.

"This was less about his family's business and an attack on his daughter," Spicer said.